This is our second version of the Mercury Bearing. The difference is in it's inside lip. The original mercury bearing's inside lip sat flush with the side, making it difficult to shim (shims sometimes touched the spining bit of the bearing in the regular Merc size C, this fixes this). We have extended this lip by .015 on each side (.030 total). This is the equivalent of using one .030 shim or two .015 shims, and it's built right into the bearing. Just by itself, this bearing widens the gap noticeably on YoYoJam yo-yos. Check out the side by side photos of regular Merc bearings and Fat Lip Merc Bearings.